(1) Physical Channels of LTE System and Method for Transmitting Signals Using the Same
FIG. 1 illustrates physical channels used in a 3rd Generation Project Partnership (3GPP) Long Term Evolution (LTE) system (Evolved Universal Terrestrial Radio Access (E-UTRA) Rel. 8 system), which is an example of a mobile communication system, and illustrates a general method for transmitting signals using the same.
When a User Equipment (UE) is powered on or has entered a new cell, the UE performs an initial cell search process, such as a process for achieving synchronization with a base station, at step S101. The UE may receive a Primary Synchronization CHannel (P-SCH) and a Secondary Synchronization CHannel (S-SCH) from the base station to achieve synchronization with the base station and to obtain information such as a cell IDentifier (ID). Thereafter, the user equipment may receive a Physical Broadcast CHannel (PBCH) from the base station to obtain intra-cell broadcasting information. On the other hand, at the initial cell search step, the UE may receive a downlink Reference Signal (RS) to check a downlink channel status.
A UE, which has completed the initial cell search, may receive a Physical Downlink Control CHannel (PDCCH) and a Physical Downlink Shared CHannel (PDSCH) corresponding to information of the PDCCH to obtain more detailed System Information (SI) at step S102.
On the other hand, a UE, which has not completed the initial cell search, may then perform a random access procedure to complete access to the base station at steps S103 to S106. To accomplish this, the UE may transmit a specific sequence as a preamble through a Physical Random Access CHannel (PRACH) (S103) and may receive a response message in response to the random access through a PDCCH and a PDSCH corresponding to the PDCCH (S104). In the case of contention-based random access, excluding the case of handover, the UE may perform a contention resolution procedure such as a procedure for transmitting an additional PRACH (S105) and receiving a PDCCH and a PDSCH corresponding to the PDCCH (S106).
When the UE has performed the above procedure, the UE may perform, as a general uplink/downlink signal transmission procedure, a procedure for receiving a PDCCH/PDSCH (S107) and transmitting a Physical Uplink Shared CHannel (PUSCH)/Physical Uplink Control CHannel (PUCCH) (S108).
(2) Random Access Scheme in LTE System
A base station manages system resources in a cellular wireless communication system. However, since it is not possible to allocate dedicated resources to a UE until the UE starts communication with the base station to be connected to the base station, the UE accesses the base station in a random access scheme in which the same wireless frequency resources are shared by a plurality of UEs in an initial access procedure. Since UEs share resources, UEs need to avoid collision of resources that they use and to discriminate cells that they desire to access. Thus, UEs use methods of discriminating resources using time, frequency, preamble, or the like.
FIG. 2 illustrates an initial random access scheme of a 3GPP LTE system.
At a 0th step (S200), a base station (eNB) broadcasts System Information (SI). Specifically, the base station broadcasts PRACH configuration information of each cell, such as available time-frequency resources and available Random Access CHannel (RACH) preamble set information, through the system information.
At a 1st step (S210), a UE transmits a PRACH preamble. Specifically, the UE receives the system information broadcast from each cell that the UE desires to access and selects and transmits an available RACH preamble in the time-frequency resources according to the system information. Here, a message in which the RACH preamble is transmitted is referred to as a “Message 1”.
At a 2nd step (S220), the base station sends a PRACH response. Specifically, the base station identifies a cell that the UE desires to access through the preamble and time-frequency resources, through which the preamble has been transmitted, and transmits an RACH response through a PDCCH addressed (or indicated) by a Random Access-Radio Network Temporary Identifier (RA-RNTI) corresponding to the time-frequency resources through which the preamble has been transmitted. Timing alignment information, initial uplink grant, temporary ID (specifically, temporary C-RNTI) allocation information, and the like are transmitted through the RACH response. The UE detects whether or not a PDCCH addressed by the RA-RNTI has been received during a specific time-interval window after the preamble is transmitted. Here, a message in which the RACH response message is transmitted is referred to as a “Message 2”.
At a 3rd step (S230), the UE performs scheduled transmission. Specifically, if preamble information transmitted by the UE is included in the RACH response received by the UE, the UE transmits a Radio Resource Control (RRC) connection request and at least a Non-Access Stratum (NAS) UE ID through a PUSCH that has been allocated to the UE through the initial uplink grant. A message in which the connection request and at least the NAS user ID are transmitted is referred to as a “Message 3”.
At a 4th step (S240), the base station transmits a contention resolution message. Specifically, the base station transmits the contention resolution message to the UE. When there is no contention, the Temporary Cell Radio Network Temporary Identity (TC-RNTI) is a Cell Radio Network Temporary Identity (C-RNTI). Thereafter, the UE detects and receives a PDCCH addressed by the C-RNTI. A message in which the contention resolution message is transmitted is referred to as a “Message 4”.
(3) Method of Signaling Carrier Frequency Band in LTE System
A 3GPP system has been designed so as to operate in frequency bands as shown in the following Table 1. Table 1 illustrates uplink and downlink frequency bands in E-UTRA.
TABLE 1Uplink (UL)Downlink (DL)E-BS receiveBS transmitDu-UTRAUE transmitUE receiveplexBandFUL—low-FUL—highFDL—low-FDL—highMode 11920 MHz-1980 MHz2110 MHz-2170 MHzFDD 21850 MHz-1910 MHz1930 MHz-1990 MHzFDD 31710 MHz-1785 MHz1805 MHz-1880 MHzFDD 41710 MHz-1755 MHz2110 MHz-2155 MHzFDD 5824 MHz-849 MHz869 MHz-894 MHzFDD 6830 MHz-840 MHz875 MHz-885 MHzFDD 72500 MHz-2570 MHz2620 MHz-2690 MHzFDD 8880 MHz-915 MHz925 MHz-960 MHzFDD 91749.9 MHz-1784.9 MHz1844.9 MHz-1879.9 MHzFDD101710 MHz-1770 MHz2110 MHz-2170 MHzFDD111427.9 MHz-1452.9 MHz1475.9 MHz-1500.9 MHzFDD12698 MHz-716 MHz728 MHz-746 MHzFDD13777 MHz-787 MHz746 MHz-756 MHzFDD14788 MHz-798 MHz758 MHz-768 MHzFDD. . .17704 MHz-716 MHz734 MHz-746 MHzFDD. . .331900 MHz-1920 MHz1900 MHz-1920 MHzTDD342010 MHz-2025 MHz2010 MHz-2025 MHzTDD351850 MHz-1910 MHz1850 MHz-1910 MHzTDD361930 MHz-1990 MHz1930 MHz-1990 MHzTDD371910 MHz-1930 MHz1910 MHz-1930 MHzTDD382570 MHz-2620 MHz2570 MHz-2620 MHzTDD391880 MHz-1920 MHz1880 MHz-1920 MHzTDD402300 MHz-2400 MHz2300 MHz-2400 MHzTDD
As illustrated in Table 1, two different frequency bands are used, respectively, in uplink and downlink in the case of Frequency Division Duplex (FDD) and one frequency band is divided in time into two sections to be used, respectively, in uplink and downlink in the case of Time Division Duplex (TDD). One frequency band (in the case of TDD) and one pair of frequency bands (in the case of FDD) are used for one cell and one base station may have a number of cells which are discriminated spatially or through different frequency bands. In the above Table 1, a channel raster is 100 KHz, which is a central frequency that the UE needs to search for when achieving synchronization with the base station at an initial stage. This indicates that the central frequency of each carrier frequency should be a multiple of 100 KHz.
The sizes of bands and carrier frequencies of uplink and downlink are defined in an E-UTRA Absolute Radio Frequency Channel Number (EARFCN) format and are transmitted through system information. In the case of FDD, different uplink and downlink bands are used in pairs and an EARFCN of the uplink band is transmitted to the UE. In the case where a number of neighboring cells which are discriminated through frequency bands are present, EARFCN information of the bands of the cells is broadcast through system information to enable handover to the cells.
The following Table 2 illustrates channel numbers of frequency bands.
TABLE 2E-UTRADownlinkUplinkBandFDL_low [MHz]Noffs-DLRange of NDLFUL_low [MHz]Noffs-ULRange of NUL 121100 0-59919201300013000-13599 21930600 600-119918501360013600-14199 3180512001200-194917101420014200-14949 4211019501950-239917101495014950-15399 586924002400-26498241540015400-15649 687526502650-27498301565015650-15749 7262027502750-344925001575015750-16449 892534503450-37998801645016450-16799 91844.938003800-41491749.91680016800-1714910211041504150-474917101715017150-17749111475.947504750-49991427.91775017750-179991272850005000-51796981800018000-181791374651805180-52797771818018180-182791475852805280-53797881828018280-18379. . .3319002600026000-2619919002600026000-261993420102620026200-2634920102620026200-263493518502635026350-2694918502635026350-269493619302695026950-2754919302695026950-275493719102755027550-2774919102755027550-277493825702775027750-2824925702775027750-282493918802825028250-2864918802825028250-286494023002865028650-2964923002865028650-29649
In Table 2, carrier frequencies (MHz) and an EARFCN for downlink satisfy the following Mathematical Expression 1.FDL=FDL—low+1(NDL−NOffs-DL)  [MATHEMATICAL EXPRESSION 1]
In Mathematical Expression 1, FDL denotes an upper frequency limit of the corresponding frequency band, FDL—low denotes a lower frequency limit of the band, NOffs-DL denotes an offset value, and NDL of the band denotes a downlink EARFCN.
In Table 2, carrier frequencies (MHz) and EARFCNs for uplink satisfy the following Mathematical Expression 2.FUL=FUL—low+0.1(NUL−NOffs-UL)  [MATHEMATICAL EXPRESSION 2]
In Mathematical Expression 2, FUL denotes an upper frequency limit of the corresponding frequency band, FUL—low denotes a lower frequency limit of the band, NOffs-UL denotes an offset value, and NUL of the band denotes an uplink EARFCN.
FIG. 3 illustrates a single component carrier of an LTE system. As shown in FIG. 3, in the case of the LTE system, transmission and reception are performed through one frequency band, and transmission and reception are performed through frequency band handover using an inter-frequency handover procedure when transmission and reception are performed through an adjacent frequency band.
FIG. 4 illustrates multiple carriers of an LTE-Advanced (LTE-A) system which is an improved version of the LTE system. In the case of the LTE-A system, one UE can simultaneously transmit and receive a plurality of Component Carriers (CC).
In the conventional LTE system, transmission and reception are performed through a single frequency band and, in the case where transmission and reception are performed through an adjacent frequency band, transmission and reception are performed using frequency band handover through an inter-frequency handover procedures.
However, the system may operate abnormally if the random access procedures of the LTE system described above is directly applied when transmission and reception are performed through a plurality of frequency bands.